Mastercard Payment Decline Code
Mastercard Decline Code 91: Authorization System or Issuer System Inoperative
Category Issuer or Network AvailabilityRetry Guidance Soft Decline (Editorial Classification)By Payment Defender Editorial TeamUpdated July 17, 2026Last reviewed July 17, 2026
What Mastercard Decline Code 91 Means
Mastercard decline code 91 (Authorization System or Issuer System Inoperative) indicates that the issuer's authorization system was unavailable when the transaction was sent. It is returned during authorization to tell the merchant the payment could not be approved as submitted.
Where the Response May Come From
Mastercard code 91 (Authorization System or Issuer System Inoperative) is returned by the issuer's authorization system during authorization and signals that the issuer's authorization system was unavailable when the request was sent. Issuers rarely disclose the precise internal cause, so treat it as a directional signal rather than a full explanation.
Common Reasons for This Response
Common causes include a temporary issuer outage, scheduled maintenance, or a system timeout. The exact trigger depends on the issuer, the account, and how the transaction was submitted, so the same code can appear in several different situations.
Should the Merchant Retry the Payment?
Because the issuer's authorization system was unavailable when the request was sent is often temporary, one retry after a short delay can succeed, but avoid rapid repeated attempts that may compound the issue and conflict with network retry expectations.
Recommended Merchant Action
Allow a brief pause and try a single retry; if the issuer's authorization system was unavailable when the request was sent continues, retry once the issuer's system is available and review the pattern with your processor.
What to Tell the Customer
Let the customer know the payment did not go through because the issuer's authorization system was unavailable when the request was sent, and suggest trying again shortly. Keep the wording neutral and avoid asserting issuer details you cannot confirm.
How to Reduce Similar Payment Failures
Segmenting how often the issuer's authorization system was unavailable when the request was sent appears by issuer and BIN, queuing retries for when issuer systems recover, and submitting clean, correctly formatted authorization data can reduce avoidable occurrences of this decline over time.
Important Limitations
Decline-code meanings vary by processor, gateway, and payment environment, and issuers do not always disclose the specific reason behind a response. The retry classification on this page is Payment Defender editorial guidance, not an official Mastercard rule. Merchants should confirm handling with their processor or gateway.
Related Decline Codes
Sources and Review Information
- PayPal (Braintree): Braintree Processor Response Codes
- Mastercard: Mastercard Rules and Merchant Support
Last reviewed July 17, 2026
Raw network-response codes are supplemental to the complete processor or gateway response. Meanings and recommended actions can vary by issuer, processor, gateway, card network, payment method, region, and merchant configuration.